1. Field of the Invention.
This invention relates to a power supply circuit for a discharge lamp, having a current limiter and a triggering device, wherein the triggering device is connected in parallel with the discharge path of the lamp formed by the lamp electrodes and has a controllable semiconductor-based electronic switch; and the invention further relates to the use of such a circuit, and a method of operating a discharge lamp.
2. Description of the Prior Art
German Patent No. 3,108,547 discloses a triggering circuit for a high pressure metal vapor discharge lamp wherein the triggering impulse is transmitted to the electrodes of the discharge path of the lamp via a pulse transformer with the aid of a symmetrically connected four-layer diode or a suitably controlled triac; in practice, such switching arrangements are usable only for triggering a.c.-powered discharge lamps and are unsuitable for d.c.-powered discharge lamps such as deuterium lamps and hydrogen lamps.
German Patent No. 3,908,553 discloses a gas discharge lamp filled with deuteriumor hydrogen gas, and methods of triggering gas discharge lamps. Alternative triggering methods described there include:
A) Triggering by applying a high voltage of, e.g., 350 V, between the anode and cathode;
B) Triggering by applying a high voltage in the range of 250 V between the anode and cathode, wherein the anode and lamp housing are interconnected via a high ohmic resistance. As long as no current flows, the anode and housing are at the same potential, so that the arc length upon triggering is shortened and thereby the breakdown voltage is reduced;
C) The triggering of the lamp is initiated by a triggering pulse applied to the lamp housing which is electrically isolated in operation, wherein an electrical arc-over is achieved between the cathode and housing with production of charge carriers which result in an arc between the anode and cathode; this method reduces the necessary triggering voltage to 100 V.
Further, German Patent No. 1,489,350 describes a gas discharge lamp filled with deuterium or hydrogen gas, which provides a device for carrying out the method described at (B), supra. This patent also discloses triggering methods for heating a bimetallic strip which in the cold state rests against and makes electrical contact with the anode and with a housing surrounding the anode, wherewith with the passage of current said strip lifts away from said housing by means of pre-ionization and glow discharge, whereupon the gas discharge lamp is triggered. Such gas discharge lamps present problems due to the relatively high heating of the gaseous contents of the bulb, wherein even with the use of relatively small openings, e.g., with diameters less than 0.5 mm, the triggering of deuterium lamps is made very difficult, and retriggering of a previously triggered gas discharge lamp is even more difficult.